Apparatus for improving the chemicothermal surface treatment of tubes

ABSTRACT

AN APPARATUS FOR HARDENING TUBULAR WORKPIECE BY ELECTRICAL GLOW DISCHARGE IN A GAS ATMOSPHERE. GAS IS DELIVERED INTO A GLOW DISCHARGE CHAMBER THROUGH A PIPE FUNCTIONING AS AN ANODE AND DISCHARGING GAS WITHIN THE TUBULAR WORKPIECE, GENERALLY MIDWAY OF ITS ENDS, THROUGH OPENINGS IN THE PIPE. BAFFLE MEANS FURTHER DEFLECT THE GAS TO EFFECT EFFICIENT DISTRIBUTION THEREOF OVER THE INTERIOR SURFACE OF THE WORKPIECE, WHICH IS CONNECTED AS A CATHODE.

July 20, 1971 H E. RORDORF 3,594,302

APPARATUS FOR IMPROVING THE CHEMICO-THERMAL SURFACE TREATMENT OF TUBESFiled June 10, 196B IN VE N TOK Ho sr EDMUND Roam/9F Mam A TTORNE YSUnited States Patent Oflice 3,594,302 Patented July 20, 1971 3,594,302APPARATUS FOR IMPROVING THE CHEMICO- THERMAL SURFACE TREATMENT OF TUBESHorst Edmund Rordorf, Weiningen, Zurich, Switzerland, assignor toElektrophysikalische Anstalt Bernhard Berghaus, Vaduz, LiechtensteinFiled June 10, 1968, Ser. No. 735,675 Int. Cl. B01k 1/00 US. Cl. 204-3122 Claims ABSTRACT OF THE DISCLOSURE Hardening by ionitriding ofworkpieces made of iron and steel means of ammonia has in many yearsbeen developed to technical perfection by the applicant and is nowestablished as a perfect hardening process with excellent qualityproperties.

Particular difficulties were met within hardening tubes, particularlygun barrels, to achieve entirely uniform hardening of the interior ofthe tube. The uneven hardening of the tube was first attributed tocertain irregularities of the glow-discharge which appeared to beirregular particularly in the interior of the tube. Accordingly, acounter-electrode was placed in the axis of the tube which was laterdesigned, according to German Pat. No. 1,141,850 of applicant, as anarrow metallic pipe passed by a coolant. However, it proved thatimperfect hardening was obtained in the interior of the tube despitethat in places, and that production losses had to be accepted.

Also known is a method of gas plating, i.e. of coating objects with athin metal film at an elevated temperature, the metal-gas compound, e.g.nickel carbonyl, being supplied to the surfaces to be metallized througha ceramic tube. However, the present invention does not relate to such agas plating method since it is based on plasmametallurgical processes.

The present invention eliminates the said disadvantages and entirelyavoids production losses.

This invention relates to a method of hardening tubes by ionitriding,particularly gun barrels, made of iron and steel, by means of anelectrical glow discharge in a metallic vacuum container with a cathodeand an anode located inside the said container, the cathode carrying theworkpiece, e.g. a gun barrel, to be hardened, and a gas supply pipe anda gas exhaust pipe. The invention is characterized by the fact that thegas employed in the treatment, particularly ammonia, is supplied to theinterior of the tube to be hardened. The invention further relates to adevice for the performance of the said method characterized by ametallic gas supply pipe passed coaxially through the center of the tubeto be hardened and closed at its interior end, the said pipe beingprovided with a plurality of nozzle-type bores from which the gas usedin the treatment can preferedly pass to the portions of the tubeinterior subject to the greatest wear, and by baflie plates arranged ata small distance in front of the gas outlet nozzles. The axial gassupply pipe may operate as the anode of the glow discharge or it mayhave no connection with the voltage source.

An embodiment of the device according to this invention is described ingreater detail with reference to the attached drawing which is alongitudinal section of a suitable vacuum container in diagrammaticrepresentation.

The container consists of the metallic wall 1 and the cover 2 and baseplates 3 secured to its in airtight relationship. The interior of thecontainer is connected to a vacuum pump (not shown) for evacuation bymeans of a gas exhaust pipe 4. Attached to a current lead-in comprisingthe metal sleeve 5, the insulator 6 and the metallic interior conductor7, which is mounted in gas-tight relationship on the cover plate 2, is aso-called centering body 8 which in turn carries the workpiece to betreated, here by way of example a steel tube 9 of which the inner wallis to be hardened. The steel tube 9 is electrically connected with theinterior conductor 7 in a suitable manner, here indicated merely by thelead 10. Arranged at the lower end of the steel tube 9 is a furthercentering body 11. The interior of the tube 9 is connected, via theopenings 12 and 13 respectively in the walls of the centering bodies 8and 11 respectively, with the interior of the container 1, 2, 3 and canthus be evacuated along with the said container. The centering bodies 8and 11 hold a metallic gas supply tube 14 which is arranged in coaxialrelationship with the steel tube 9 and connected, in the upper centeringbody 8, with the elbow 15 which leads to the insulated gas lead-in,arranged in air-tight relationship in the cover plate 2, which comprisesthe metal sleeve 16, the insulating ring 17 and the connection pipe 18.Located in the wall of the gas lead-in 14 are lateral bores 19,preferably in the vicinity of such portions of the tube interior whichshould be most reliably and durably hardened, here, by way of example,in the central area of the steel tube 9. The bores 19 are covered by ametal sleeve 20 enclosing them at a small distance. These bafiie platesprevent a gas jet emerging from the nozzle-type bores 19 from directlyimpinging on the inner wall of the steel tube 9. The gas supply tube 14is closed at its lower end or beyond the last bore 19; by way of exampleit is designed, in its lower portion, as a cylindrical bar which is heldby the centering body 11. When gas for the treatment, e.g. ammonia, issupplied through the connection 18 and removed via the exhaust 4, a gasflow enters the interior of the tube 9 through the nozzle-type bores 19,the baffle plates 20 deflecting it in the direction indicated by thebroken lines.

In order to obtain hardening of the inner wall of the tube 9 byionitriding in a nitrogenous gas atmosphere, an electrical glowdischarge must be produced in the interior of the tube 9 in addition tomaintaining a suitable underpressure in the container 1, 2, 3 and acontinuous supply of nitrogenous gas via the connecting pipe 18. In theembodiment shown, the interior conductor 7 of the current lead-in isconnected to the negative pole; the connecting pipe 18, with thepositive pole of a voltage source 22 having a suflicient voltage.

The conventional supply of the treating gas to the container, as by asupply pipe in its cover plate leading into the interior of thecontainer in which the tubes to be treated are located, causes the gasto permeate the entire space but fails sufficiently to penetrate intothe interior of the tube so as to ensure an adequate supply of nitrogento the inner portions of the tube. Only the arrangement, according tothis invention, of nozzle-type bores in the interior of the tube, fromwhich the treating gas can emerge, is directly supplied to the tubeareas to be hardened and causes a gas flow in the interior of the tubebrought as surprising improvement and enabled flawless production. Thegas supply pipe may be connected, as is the case in the embodimentrepresented, as the anode of the electrical glow discharge. If severaltubes are treated simultaneously with three-phase AC in a container, theindividual gas supply pipes may be interconnected so as to ensure aneven gas supply, no electrical connection with the voltage source beingrequired. As it emerges from the nozzles, the gas is already pre-ionizedand preheated so that it very intensively acts upon the inner wall ofthe tube connected to form the cathode and produces the hardeningeffect. In order to avoid excessive gas supplies to the tube portionslocated opposite the nozzles, it has proved to be advantageous toarrange the bafiie plates described in front of the nozzle mouths.

The device may naturally be designed in a manner different from theembodiment shown, particularly in respect of the suspension of the tubesand the attachment of the gas supply pipes. By way of example, thecentering bodies 8 and 11 may be formed of a metallic sleeve in which aninsulating body carrying the gas supply pipe is located, the said bodybeing protected against the attack of the destructive ionized gases inthe inside of the tube 9 in the known manner by a narrow protective gap;in that case, the elbow 15 of the upper centering body 8 must beinsulatedly passed through the metal sleeve and the insulating materialprotected by narrow gaps at this point as well.

What is claimed is:

1. Apparatus for hardening, by ionitriding, the interior surface of atube formed of iron and steel by means of an electrical glow dischargein gas in a metallic vacuum container having a cathode and an anodetherein, comprising:

means on said cathode for holding said tube in said container;

a gas supply pipe positioned to extend axially within and spaced fromthe sides of the tube held by said cathode, said gas supply pipe havinggas discharge means intermediate the ends of said tube;

a gas exhaust conduit leading from said container, the interior of saidcontainer being in communication with opposite ends of said tube; and

said gas supply pipe comprising said anode.

2. Apparatus as defined in claim 1 wherein the inner end of said gassupply pipe is closed;

said gas discharge means comprising nozzle-type openings in the sides ofsaid pipe adjacent said closed end for directing gas therefrom generallyradially outwardly toward the inner surface of said tube; and

baffle means, of limited area, between said openings and said tube toprevent direct impingement of gas jets from said openings onto thesurface of said tube.

References Cited UNITED STATES PATENTS 2,927,231 3/1960 Bucek l48-16.5

JOHN H. MACK, Primary Examiner N. A. KAPLAN, Assistant Examiner US. Cl.X.R.

204l77; l48l6.6

